An eclipse occurs when one object in space blocks an observer from seeing another object in space. From Earth there are two main types of eclipses: Solar eclpses and lunar eclipses.
The Temple of the Sun (Tin Tin comic)
A solar eclipse occurs when the Moon passes in front of the Sun causing a shadow to fall on certain portions of the Earth. The eclipse is not seen from every place on Earth, but only from the locations where the shadow falls. From these location, it appears as if the Sun has gone dark.